Is she pissed off about all the children he murdered, or that he confused her with a Brit king?

I'd say... Everything he's done?

I'm gonna bet on the confusing a king for her on the fact of tsunderes being crazy jealous and what not.
By the way, I have no clue about her real personality, I'm just assuming out the wazoo.

From the bio on her for Fate/Apocrypha hints towards her personality:

CoCoMoo said:
From the bio on her for Fate/Apocrypha hints towards her personality:

"She is taciturn and cool when acting as a Servant, but her natural self is a plain and quiet sixteen-year-old girl. She puts order first, and will wield a sword for the sake of the rules, but fundamentally believes "all people and Heroic Spirits participating in the Holy Grail War are important."

However, Jeanne and Gils were allies and friends. So her being mad at him for what he's done after they parted... yeah.

By His grace Gill ! I only die for a few years and you start acting like Gil ?! What is wrong with you !

AlsoSprachOdin said:
Is she pissed off about all the children he murdered, or that he confused her with a Brit king?

Hey in his defense said King looks A LOT like her only with shorter hair, and hey maybe she just decided to style her hair differently as a Servant?

Emporer-Wakamoto said:

Hey in his defense said King looks A LOT like her only with shorter hair, and hey maybe she just decided to style her hair differently as a Servant?

S A B E R F A C E triggering